docs: def dct(data):
      """
      Compute DCT using FFT
      """
      N = len(data)//2
      fftdata     = fftpack.fft(data, axis=0)[:N+1]
      fftdata     /= N
      fftdata[0]  /= 2.
      fftdata[-1] /= 2.
      if np.isrealobj(data):
          data = np.real(fftdata)
      else:
          data = fftdata
      return data